1. Field of Invention
The invention relates to a method and an apparatus for determining the concentration of a liquid ice mixture.
2. Description of the Prior Art
Liquid ice mixtures comprise suspensions or mixtures of ice crystals or ice fragments in liquid (hereinafter called "binary ice fluid"). Such two-phase fluids are used for cold transport, storage and use. With respect to such fluids it is important to precisely know the ice concentration in order to maintain and/or determine all the process parameters in installations where such liquid ice mixtures are used. It is difficult to precisely determine the ice concentration in a binary ice fluid. The determination of the ice concentration by measuring the electrical conductivity, as known from DE 43 25 793 C2, is not very accurate and cannot be used for any random liquid. Viscosity measurements are difficult to perform even when possible. The pressure drop over a fixed distance is also not a suitable signal, because the viscosity of the liquid is based on the temperature, quantity and quality of additives.
The reason for the use of a binary ice fluid is the latent energy (enthalpy of fusion) of the ice contained in the fluid. This makes it possible to reduce pipeline cross-sections, reduce pumping energy and reduce the size of energy storage devices and heat exchanger surfaces.
The latent energy of binary ice cannot be determined with temperature sensors, because the temperature of the binary ice in the melting range does not or only just changes. Thus, another way for determining the ice concentration is required.
Normally the ice concentration of binary ice is determined by the "calorimetric" method. A volume of binary ice is weighed and its temperature determined. A second volume of sufficiently warm fluid (e.g. water) is weighed and its temperature determined. The two volumes are then mixed and it is then possible by means of the mixture temperature to back-calculate the ice concentration, provided that the mixture no longer contains ice.
However, this method is discontinuous, time-consuming and is only suitable for manual utilization on a laboratory scale.
It is known from DE 43 25 794 C1 to determine the ice concentration in a fluid mixture by measuring the pressure exerted by it.
The problem of the invention is to provide a method and an apparatus for determining the concentration of a liquid mixture, which is applied to a pipeline and which can determine the concentration at least in short intervals.